Day 6: Modules, Standard Library Suggested reading: Learning Python - PowerPoint PPT Presentation

Computer Sciences 368 Scripting for CHTC Day 6: Modules, Standard Library Suggested reading: Learning Python (4th Ed.) Ch.21: Modules: The Big Picture Ch.22: Module Coding Basics http://docs.python.org/release/2.4.3/modindex.html 2012 Fall Cartwright 1

Computer Sciences 368 Scripting for CHTC Turn In Homework 2012 Fall Cartwright 2

Computer Sciences 368 Scripting for CHTC Homework Review 2012 Fall Cartwright 3

Computer Sciences 368 Scripting for CHTC Modules 2012 Fall Cartwright 4

Computer Sciences 368 Scripting for CHTC Python Module = .py File 2012 Fall Cartwright 5

Computer Sciences 368 Scripting for CHTC Why Write a Module? • Maximize code reuse / Minimize code redundancy • Organize code clearly (group related definitions) • Make testable units of code • Share data among separate script parts (Does this list look familiar?) 2012 Fall Cartwright 6

Computer Sciences 368 Scripting for CHTC Importing a Module import module_name 1. Looks up or else creates module object 2. Assigns object to module_name 3. Runs all top-level code in module! 4. Objects are bound to names in module namespace: – variables (via = ) – functions (via def ) – classes (via class ) – other modules (via import ) 2012 Fall Cartwright 7

Computer Sciences 368 Scripting for CHTC Accessing Module Parts module_name . attribute • Same as accessing parts of an object • Because a module is an object, which is a namespace foo.py: bar.py: import math import foo f = 42 print foo.math.pi def circum(mult): foo.f += 2 d = 2 * f * mult x = foo.circum(2) return d * math.pi 2012 Fall Cartwright 8

Computer Sciences 368 Scripting for CHTC Sample Module I _c2f_ratio = 5.0 / 9.0 # "private"-ish _f2c_ratio = 9.0 / 5.0 # "private"-ish def convert_c2f(deg_f): return (deg_f – 32.0) * _c2f_ratio def convert_f2c(deg_c): return (deg_c * _f2c_ratio) + 32.0 import temp_convert f = 70.0 c = temp_convert.convert_f2c(f) print "%.1f F = %.1f C" % (f, c) 2012 Fall Cartwright 9

Computer Sciences 368 Scripting for CHTC Sample Module II import csv datafile = 'results.csv' def load(): results = [] r = csv.reader(open(datafile, 'rb')) for row in reader: results.append(row) return results def write(data): # ... 2012 Fall Cartwright 10

Computer Sciences 368 Scripting for CHTC Standard Library 2012 Fall Cartwright 11

Computer Sciences 368 Scripting for CHTC 2012 Fall Cartwright 12

Computer Sciences 368 Scripting for CHTC Built-In Functions 2012 Fall Cartwright 13

Computer Sciences 368 Scripting for CHTC Review … and Some New Friends bool float int long str - dir help chr hex oct ord - len range - id type abs max min pow round sum - raw_input chr(97) => 'a' ord('a') => 97 max(1, 2, 3, 4, 5) => 5 round(2.5) => 3.0 sum(range(1, 101)) => 5050 2 is (1 + 1) => True id(2), id(1 + 1) => ( 437788320 , 437788320 ) 2012 Fall Cartwright 14

Computer Sciences 368 Scripting for CHTC Sorting Sort a list object in place : list .sort(cmp, key, reverse) # all opt. names = ['Tim', 'Alain', 'scot', 'mat'] def lcmp(x, y): return cmp(x.lower(), y.lower()) names.sort() names.sort(cmp=lcmp) names.sort(key=str.lower, reverse=True) Sort any iterable object and make new list object: new_list = sorted(list, cmp, key, reverse) 2012 Fall Cartwright 15

Computer Sciences 368 Scripting for CHTC Transforming map( function , iterable , ...) >>> map(chr, range(65, 91)) ['A', 'B', 'C', …, 'Y', 'Z'] >>> map(str.capitalize, ('tim', 'mAt', …)) ['Tim', 'Mat', …] def mult(x, y): return x * y a = (2, 3, 6, 4, 8) b = (12, 8, 4, 6, 3) twentyfour = map(mult, a, b) 2012 Fall Cartwright 16

Computer Sciences 368 Scripting for CHTC Filtering filter( function , iterable ) >>> t = ('Hi!', '42', '4.0', '-1', '1001') >>> filter(str.isdigit, t) ('42', '1001') def large(t): return t[1] > 100.0 p = {'cn': 1339.7, 'ph': 94.0, 'dk': 5.6, 'us': 312.5, 'in': 1210.2, 'ki': 0.1} big = dict(filter(large, p.items())) 2012 Fall Cartwright 17

Computer Sciences 368 Scripting for CHTC Numbers 2012 Fall Cartwright 18

Computer Sciences 368 Scripting for CHTC math pi e - ceil floor fmod fabs cos sin tan - degrees radians exp factorial log log10 pow sqrt 2 * math.pi => 6.283185307179586 math.log(math.e) => 1.0 math.ceil(2.5) => 3.0 math.floor(2.5) => 2.0 math.cos(1.0) => 0.5403023058681398 math.degrees(0.54) => 30.939720937064457 math.sqrt(90.0) => 9.486832980505138 2012 Fall Cartwright 19

Computer Sciences 368 Scripting for CHTC decimal • Does exact decimal floating point math • Has pros and cons compared to regular floats • Very useful for fixed-decimal math (e.g., finance) >>> 0.1 + 0.1 + 0.1 - 0.3 5.551115123125783e-17 >>> import decimal >>> Decimal('0.1') + Decimal('0.1') + \ ... Decimal('0.1') - Decimal('0.3') Decimal('0.0') >>> print Decimal('0.0') 0.0 2012 Fall Cartwright 20

Computer Sciences 368 Scripting for CHTC random random uniform gauss normalvariate … randint choice shuffle sample - seed random.random() => 0.26510474670383377 random.random() => 0.09321673054441892 random.normalvariate(100, 10) => 95.3900… random.randint(1, 100) => 42 x = range(1, 6) random.shuffle(x) x => [2, 4, 1, 5, 3] random.choice(['A', 'B', 'C', 'D']) => 'A' 2012 Fall Cartwright 21

Computer Sciences 368 Scripting for CHTC Dates and Times 2012 Fall Cartwright 22

Computer Sciences 368 Scripting for CHTC time time - localtime gmtime asctime strftime - mktime strptime >>> time.time() 1319402100.752616 >>> time.localtime() time.struct_time(tm_year=2011, tm_mon=10, tm_mday=23, tm_hour=15, tm_min=35, tm_sec=20, tm_wday=6, tm_yday=296, tm_isdst=1) >>> time.asctime() 'Sun Oct 23 15:36:51 2011' >>> time.strftime('%d %B %Y - %H:%M') '23 October 2011 - 15:36' 2012 Fall Cartwright 23

Computer Sciences 368 Scripting for CHTC datetime • Complex set of classes for date/time calculations • Extra code required to handle timezones correctly from datetime import datetime, timedelta start = datetime.now() wait = timedelta(weeks=1, hours=8) then = start + wait print then.strftime('%m/%d @ %H:%M') 2012 Fall Cartwright 24

Computer Sciences 368 Scripting for CHTC calendar • Mostly for printing fixed-width text calendars • Does a few other date calculations >>> calendar.prmonth(2011, 11) November 2011 Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 2012 Fall Cartwright 25

Computer Sciences 368 Scripting for CHTC Files 2012 Fall Cartwright 26

Computer Sciences 368 Scripting for CHTC csv Tim Cartwright,4265,2-4002,"CHTC, OSG" Alain Roy,4261,5-5736,"CHTC, OSG" Greg Thain,4279,0-0031,CHTC • Used by Excel and others • Wildly inconsistent, non-standardized format • Hard to parse yourself, use the module instead • Can o ff er hints as to particular CSV format file = open( csv_file , 'rb') reader = csv.reader(file) for row in reader: # row is list, 1 item/CSV field 2012 Fall Cartwright 27

Computer Sciences 368 Scripting for CHTC fnmatch fnmatch fnmatchcase filter file = raw_input('Enter filename: ') if not fnmatch.fnmatch(file, '*.html'): print 'Please enter an HTML file!' files = os.listdir('.') for file in fnmatch.filter(files, '*.py'): print 'Python file:', file 2012 Fall Cartwright 28

Computer Sciences 368 Scripting for CHTC glob • Acts like shell wildcards • Uses fnmatch for implementation for pth in glob.glob('travel/201?/*.csv'): print 'Recent travel table:', pth file = open(pth, 'rb') reader = csv.reader(file) # ... 2012 Fall Cartwright 29

Computer Sciences 368 Scripting for CHTC The System 2012 Fall Cartwright 30

Computer Sciences 368 Scripting for CHTC sys stdin stdout stderr - platform version getrefcount - modules - path prefix getsizeof float_info long_info maxint plus lots more! sys.platform => 'linux2' sys.version_info => (2, 4, 3, 'final', 0) sys.getrefcount(2) => 33 sys.getrefcount(1234) => 2 sys.maxint => 2147483647 len(sys.modules) => 30 2012 Fall Cartwright 31

Computer Sciences 368 Scripting for CHTC os chdir getcwd - readlink symlink unlink chmod chown stat - remove rename makedirs mkdir rmdir - listdir walk plus lots more! for t in os.walk( path ): # t = (dirname, subdirs, files) for f in t[2]: if fnmatch.fnmatch(f, '*.py'): print 'Py:', os.path.join(t[0], f) 2012 Fall Cartwright 32

Computer Sciences 368 Scripting for CHTC os.path abspath realpath basename dirname join split exists isdir isfile islink getatime getctime getmtime getsize dir = 'wibble/wobble' file = raw_input('File? ') path = os.path.join(dir, file) if os.path.exists(path) and \ os.path.getsize(path) > 0: print 'Path:', os.path.abspath(path) print 'Size:', os.path.getsize(path) print 'Mod:', os.path.getmtime(path) 2012 Fall Cartwright 33